The present invention relates to a brake booster, which boosts operating force exerted on an operating means with working fluid pressure, that is controlled by a control valve, into predetermined magnitude to output intensified force and, more particularly, to a brake booster which can set the input travel variously without being affected by the operation of a working unit of a master cylinder and the like operated with the output of the brake booster and can control the output of the brake booster during its operation regardless of the operating force exerted on the operating means.
For example, in a conventional brake system of an automobile, a brake booster has been employed which boosts pedaling force exerted on a brake pedal by fluid pressure of hydraulic fluid into predetermined magnitude to develop large brake fluid pressure. The brake booster functions to provide large braking force from small pedaling force exerted on the brake pedal, thereby securing the braking action and reducing the labor of a driver.
Such conventional brake booster can be roughly classified into a vacuum booster for boosting the pedaling force by negative pressure to actuate the master cylinder, a hydraulic booster for boosting the pedaling force by fluid pressure to actuate the master cylinder, a full-power brake system in which the fluid pressure is directly supplied to the wheel cylinders, and a pneumatic/electromagnetic booster for boosting the pedaling force by compressed air/electromagnetic force to actuate the master cylinder.
FIG. 22 is a schematic illustration of a brake system employing a conventional vacuum booster and FIG. 23 is a schematic illustration of a brake system employing a conventional hydraulic booster.
In the brake system employing the vacuum booster shown in FIG. 22, input force Fi is exerted to an input shaft 4 by depression of a brake pedal 3 so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is shut off from a low-pressure (L) valve passage 5b1 of a second valve element 5b connected to a negative pressure source and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to the atmospheric air. The atmospheric air is controlled according to the input Fi by the control valve 5 to develop output pressure Pr. The output pressure Pr is supplied to a power chamber 10c of the power cylinder 10 so that a power piston 10b moves to the left to produce output Fp which is boosted pedaling force. A master piston 11a is actuated by the output Fp so that a master cylinder 11 develops master cylinder pressure Pm which is supplied to wheel cylinder 7 as braking fluid pressure Pb, thereby actuating the brake. Reaction force Fm from the master cylinder 11 is modulated as reaction force Fv by a reaction mechanism 8 and is applied to the first valve element 5a. Therefore, the output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force Fi of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3. In the vacuum booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 10b. 
In the break system employing the hydraulic booster shown in FIG. 23, input force Fi is exerted to an input shaft 4 by depression of a brake pedal 3 so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is shut off from a low-pressure (L) valve passage 5b1 of a second valve element 5b connected to a reservoir and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to a fluid pressure source. The hydraulic pressure of the fluid pressure source such as a pump and an accumulator is controlled according to the input Fi by the control valve 5 to develop output pressure Pr. The output pressure Pr is supplied to a power chamber 10c of the power cylinder 10 so that a power piston 10b moves to the left to produce output Fp which is boosted pedaling force. A master piston 11a is actuated by the output Fp so that a master cylinder 11 develops master cylinder pressure Pm which is supplied to wheel cylinder 7 as braking fluid pressure Pb, thereby actuating the brake. Reaction force Fm from the master cylinder 11 and reaction force by the output pressure Pr of the control valve 5 are modulated as reaction force Fv by a reaction receiving portion and is applied to the first valve element 5a. Therefore, the output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force Fi of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3. In the hydraulic booster, in the same manner as the vacuum booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 10b. 
By the way, such conventional brake systems employ various brake controls such as for controlling the braking force during the braking action, for example, Brake Assist Control for increasing the braking force when the braking force is insufficient for emergency brake or the like, and Regenerative Brake Coordination Control to be performed when a regenerative brake system is used to develop braking pressure during the braking action by the service brake system, and automatic brake controls, for example, a brake control for controlling the distance from a vehicle in front, a brake control for avoiding a collision with an obstacle object, and Traction Control (TRC).
Most of such brake controls are normally conducted in a brake circuit between the master cylinder and the wheel cylinders. However, when the brake control is conducted in the brake circuit after the master cylinder, it is required to prevent the travel of the brake pedal or pedaling force from being affected by such brake controls, for instance, for obtaining better operational feeling.
However, in a conventional brake system, the travel of a piston of the master cylinder is fixed by the relation between the master cylinder and wheel cylinders or the relation between the master cylinder and the stroke simulator so that the stroke of an input shaft of the brake booster, i.e. the pedal travel of a brake pedal, depends on the travel of the piston of the master cylinder. That is, the travel for input is affected by the brake controls conducted in the brake circuit after the master cylinder. In the conventional brake system, the aforementioned requirement can not be securely and sufficiently satisfied.
For changing the travel characteristic of the brake pedal as the input side to obtain better operational feeling, the master cylinder and the brake circuit after the master cylinder are also affected so that some modifications on the output side, for instance a size change on the master cylinder, should be required. By the change on the output side, the output characteristic of the brake system is affected. This means that the overall modification on the brake system is required, i.e. large-scale modification is required.
It is further desired that the input side is affected as little as possible by brake circuit which may differ according to the type or size of vehicle.
If the input side and the output side are just separated from each other to produce outputs regardless of the travel of the input side, the input side does not travel so that the travel of the input side can not be ensured.
For this, a full power brake system has been conventionally proposed in which a stroke simulator is provided on the brake circuit after the master cylinder to prevent the travel of the input side from being affected by the brake control after the master cylinder and to ensure the travel of the input side.
This type of full power brake system is shown in FIG. 24, and input force Fi is exerted to an input shaft 4 by depression of a brake pedal 3 so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is shut off from a low-pressure (L) valve passage 5b1 of a second valve element 5b connected to a reservoir and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to a fluid pressure source. The hydraulic pressure of the fluid pressure source such as a pump and an accumulator is controlled according to the input Fi by the control valve 5 to develop output pressure Pr. The output pressure Pr is supplied to wheel cylinder 7 as braking fluid pressure Pb, thereby actuating the brake. At the same time, the output pressure Pr is also supplied to a power chamber 10c of the power cylinder 10 so that the power piston 10b moves to the left to produce output Fp. The master piston 11a is actuated by the output Fp so that the master cylinder 11 develops master cylinder pressure Pm which is supplied to the stroke simulator 19 whereby the stroke simulator 19 moves to the left, thereby ensuring the travel of the input shaft 4, i.e. the travel of the first valve element 5a. Reaction force Fm from the master cylinder 11 and reaction force by the output pressure Pr of the control valve 5 are modulated as reaction force Fv by a reaction receiving portion and are applied to the first valve element 5a. Therefore, the output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force Fi of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3. In this full power brake system, in the same manner as the vacuum or hydraulic booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 10b. 
However, to prepare the additional stroke simulator, many parts such as a stroke cylinder and an electromagnetic switching valve used for the stroke simulator are required, making the structure complex and increasing the cost.
There is still a problem that the brakes must be securely actuated in case of a fluid pressure source failure even when a stroke simulator is provided.
In a regenerative coordination brake system composed of a combination of a service brake system and a regenerative brake system, when the regenerative brake system is operated during the operation of the brake booster, the braking force produced by the brake booster should be reduced for the braking force produced by the regenerative brake system. In this case, it is desired to reduce the output of the brake booster to a value obtained by subtracting the output of the regenerative brake system from the output of the brake booster. In a brake system composed of a combination of a service brake system and a brake assist system, it is desired to increase the output of the brake booster to intensify the braking force produced by the brake booster in such case that brake assist operation is needed, for example, a case that a driver can not depress a brake pedal enough during the operation of the brake booster so as not to produce predetermined braking force.
It is desired that the brake pedal is not affected by the brake control when performed during the braking action.
Further, in a brake system for controlling the distance from a vehicle in front, a control for holding the distance constant is conducted by automatically actuating the brake when the distance becomes short during running. In a brake system for avoiding a collision, a control for avoiding a collision with an obstacle object is conducted by automatically actuating the brake when there is a possibility of collision with the obstacle object. Furthermore, in a traction control system, a control for cancelling a slipping tendency is conducted to ensure the secure starting by automatically braking driving wheels when the driving wheel(s) is in slipping tendency at the starting.
It is desired that the brake pedal is not affected when the automatic braking is conducted as mentioned above.
Further, it is desired that such a system for controlling the braking force during braking action or controlling the automatic braking can be manufactured with a simple structure.
Moreover, it is desired that the input versus travel characteristic, the input versus braking pressure characteristic, or the travel versus braking pressure characteristic is allowed to be varied according to the condition of a vehicle with a simple structure.
It is an object of the present invention to provide a brake booster in which a brake operating means is not affected or is hardly affected by the control of the braking force when performed during the braking action.
It is another object of the present invention to provide a brake booster of which the input-output characteristics such as the input versus braking pressure characteristic, the input versus travel characteristic, or the travel versus braking pressure characteristic is allowed to be varied without large-scale modification.
It is still another object of the present invention to provide a brake booster of which the output can be controlled regardless of the input of an input member during operation.
It is yet another object of the present invention to provide a brake booster which can achieve the aforementioned objects and still can be small-sized and inexpensive.
It is still yet another object of the present invention to provide a brake booster which can achieve the aforementioned objects and still allows the brakes to be securely actuated in case of a fluid pressure source failure.
To achieve the aforementioned objects, the present invention provides a brake booster comprising at least a housing, an input shaft which is actuated by input applied through the operation of a brake operating means, and a control valve which is disposed in said housing and is operated by the actuation of said input shaft to regulate the pressure of a pressure source according to the operational input (operating travel, operating force) of the brake operating means to output the regulated pressure, wherein said control valve has at least a first valve element and a second valve element, said first valve element is moved relative to said second valve element by the actuation of said input shaft and is subjected to the output pressure of said control valve in a direction opposite to the actuating force of said input shaft, and said second valve element is fixed to said housing, the brake booster being characterized by further comprising an operational input converting means which is disposed between said input shaft and said first valve element and is at least partially displaced by the input of said input shaft to convert the operational input of said brake operating means to actuating force for actuating said first valve element, and characterized in that the output pressure of said control valve acts on said input shaft in the direction opposite to the operational input of said brake operating means.
The brake booster of the present invention is characterized in that said operational input converting means comprises an elastic member disposed between said input shaft and said first valve element, and said elastic member converts the operational input of said brake operating means to said actuating force and transmits said actuating force to said first valve element.
Further, the brake booster of the present invention is characterized in that said operational input converting means comprises a displacement detector for detecting displacement of said input shaft, and an actuator for actuating said first valve element according to a signal from said displacement detector.
Further, the brake booster of the present invention is characterized in that said operational input converting means has a stroke means which travels according to the displacement of said input shaft.
The brake booster of the present invention is characterized by further comprising a power cylinder which is operated by the output pressure of said control valve to develop braking pressure.
The brake booster of the present invention is characterized by further comprising an operating member which is disposed on said input shaft to actuate said power cylinder by way of the operation of said brake operating means when said pressure source fails.
The present invention further provides a brake booster comprising at least a housing, an input shaft which is actuated by input applied through the operation of a brake operating means, and a control valve which is disposed in said housing and is operated by the actuation of said input shaft to regulate the pressure of a pressure source according to the operational input (operating travel, operating force) of the brake operating means to output the regulated pressure, wherein said control valve has at least a first valve element and a second valve element, said first valve element is moved relative to said second valve element by the actuation of said input shaft and is subjected to the output pressure of said control valve in a direction opposite to the actuating force of said input shaft, and said second valve element is fixed to said housing, said brake booster being characterized by further comprising an operational input converting means which is disposed between said input shaft and said first valve element and is at least partially displaced by the input of said input shaft to convert the operational input of said brake operating means to actuating force for operating said first valve element according to the operational input, and a characteristic varying means for allowing the input and output characteristics to be varied.
The brake booster is characterized in that said characteristic varying means has a pressure regulating valve which regulates the output pressure of said control valve or the pressure of said pressure source to output regulated pressure that acts on said first valve element in a direction opposite to the actuating force of the input shaft.
The brake booster is characterized in that said characteristic varying means has a pressure regulating valve which regulates the output pressure of said control valve or the pressure of said pressure source to output regulated pressure that acts on said input shaft in a direction opposite to the operation of said brake operating means.
Further, the brake booster is characterized in that said characteristic varying means has a pressure regulating valve which regulates the output of said control valve or the pressure of said pressure source to output regulated pressure whereby the output of said brake booster is produced.
Furthermore, the brake booster is characterized in that said characteristic varying means has a reaction force producing means which produces a reaction force acting on said first valve element in a direction opposite to the actuating force of said input shaft.
Still further, the brake booster is characterized in that said operational input converting means has a stroke means which travels according to the displacement of said input shaft and said characteristic varying means has a stroke varying means for varying said travel of said stroke means.
In the brake booster of the present invention structured as mentioned above, the input side and the output side thereof can be separated. Therefore, when the control of the braking force is conducted in the brake circuit between the control valve and the brake cylinder during the braking action, the brake operating means tis not affected or at least hardly affected by this control of the braking force.
Further, without being affected by the output side of the brake booster, the input versus braking pressure characteristic, the input versus travel characteristic, or the travel versus braking pressure characteristic can be varied without large-scale modification.
Furthermore, regardless of the input of the input side during the braking action, the control of the braking force can be conducted in the brake circuit between the control valve and the wheel cylinders. Accordingly, the brake booster can be easily and flexibly adopted to such system in which the control of the braking pressure is required during the operation of the brake booster regardless of the operation of the brake operating means, for instance, the control for reducing the braking pressure to be conducted during the operation of a regenerative brake system with a regenerative brake coordination control, and the control for increasing the braking pressure to be conducted during the brake assisting operation by a brake assist system.
Moreover, the operational input converting means moves when converting the pedal input into the actuating force, thereby ensuring the operational travel of the brake operating means. This means that the operational input converting means exhibits the same function as a conventional stroke simulator.
Furthermore, since an elastic member such as a spring or an actuator which detects the displacement of the input shaft and operates according to the displacement detected is employed as the operational input converting means, the brake booster can be small-sized and inexpensive.
In addition, the brake booster allows the brakes to be securely actuated even when the pressure of the pressure source fails.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.